Mutations of the type IV collagen alpha 1 gene (Col4a1) cause highly penetrant ocular anterior segment dysgenesis (ASD) and elevated intraocular pressure in mice. Recently, a COL4A1 mutation was identified in a family with ASD, ocular hypertension and juvenile glaucoma, however, COL4A1, has not widely been considered a candidate gene for ASD. In this proposal we identify the contribution of COL4A1 and COL4A2 to human ASD and will use novel genetic resources to determine the cellular and molecular mechanisms of Col4a 1-induced ASD. COL4A1 is an extracellular matrix molecule that is present in all ocular basement membranes. To understand where and when the pathogenic insult occurs we have developed a conditionally expressed mutant allele of Col4a1. In Aim 1 we will express the mutant allele in a spatially or temporally restricted manner to define these parameters and determine the primary site of pathogenesis. To understand the mechanism by which Col4a1 mutations lead to ocular dysgenesis and to begin to assemble developmental and pathogenic pathways, we will identify genetic modifiers of ASD. We have already successfully mapped a locus that is able to strongly rescue ASD. In Aim 2, we will perform systematic large-scale screens of two distinct genetic backgrounds to identify additional dominant or recessive modifier loci and genes. Understanding how genetic modifiers rescue disease could provide valuable insight for how targeted therapeutic interventions might do the same. Importantly, a COL4A1 mutation was identified in a family with ASD, ocular hypertension and juvenile glaucoma. We hypothesize that mutations of COL4A1 and its binding partner COL4A2 underlie ASD in patients for whom mutations have not yet been identified. In Aim 3, we will test our hypothesis directly by performing mutational analysis on ASD patients that are known not to have mutations in other ASD-causing genes. To our knowledge, no other group is currently evaluating the role of COL4A1 or COL4A2 in ocular development and disease. The experiments outlined in this proposal take advantage of valuable and unique resources and will provide important new insights into the mechanisms of normal ocular development and pathogenic pathways.